The average process stream outlet humidity ratio of an adiabatic counterflow dehumidifier can be lowered if a portion of the process outlet stream is purged from the bulk flow. The purged stream can be recirculated and introduced at the inlet of the regenerating period. In this paper, the performance of such a purged counterflow dehumidifier is studied. Two purge geometries that result in a spatially nonuniform inlet condition in the regenerating period are considered. Wave diagram solutions for the limiting case of infinite heat and mass transfer coefficients are used to qualitatively predict the behavior of the purged dehumidifier. A finite difference solution is used to verify the general trends of the approximate wave diagram solutions. The effect of the recirculated purge on the process stream outlet states of high performance silica gel dehumidifiers with low and high thermal capacitance matrices operated at nearly optimal rotational speeds is evaluated.

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